## lib/trollop.rb -- trollop command-line processing library
## Author::    William Morgan (mailto: wmorgan-trollop@masanjin.net)
## Copyright:: Copyright 2007 William Morgan
## License::   the same terms as ruby itself

require 'date'

module Trollop

  VERSION = "2.0"

## Thrown by Parser in the event of a commandline error. Not needed if
## you're using the Trollop::options entry.
  class CommandlineError < StandardError; end

## Thrown by Parser if the user passes in '-h' or '--help'. Handled
## automatically by Trollop#options.
  class HelpNeeded < StandardError; end

## Thrown by Parser if the user passes in '-h' or '--version'. Handled
## automatically by Trollop#options.
  class VersionNeeded < StandardError; end

## Regex for floating point numbers
  FLOAT_RE = /^-?((\d+(\.\d+)?)|(\.\d+))([eE][-+]?[\d]+)?$/

## Regex for parameters
  PARAM_RE = /^-(-|\.$|[^\d\.])/

## The commandline parser. In typical usage, the methods in this class
## will be handled internally by Trollop::options. In this case, only the
## #opt, #banner and #version, #depends, and #conflicts methods will
## typically be called.
##
## If you want to instantiate this class yourself (for more complicated
## argument-parsing logic), call #parse to actually produce the output hash,
## and consider calling it from within
## Trollop::with_standard_exception_handling.
  class Parser

    ## The set of values that indicate a flag option when passed as the
    ## +:type+ parameter of #opt.
    FLAG_TYPES = [:flag, :bool, :boolean]

    ## The set of values that indicate a single-parameter (normal) option when
    ## passed as the +:type+ parameter of #opt.
    ##
    ## A value of +io+ corresponds to a readable IO resource, including
    ## a filename, URI, or the strings 'stdin' or '-'.
    SINGLE_ARG_TYPES = [:int, :integer, :string, :double, :float, :io, :date]

    ## The set of values that indicate a multiple-parameter option (i.e., that
    ## takes multiple space-separated values on the commandline) when passed as
    ## the +:type+ parameter of #opt.
    MULTI_ARG_TYPES = [:ints, :integers, :strings, :doubles, :floats, :ios, :dates]

    ## The complete set of legal values for the +:type+ parameter of #opt.
    TYPES = FLAG_TYPES + SINGLE_ARG_TYPES + MULTI_ARG_TYPES

    INVALID_SHORT_ARG_REGEX = /[\d-]/ #:nodoc:

    ## The values from the commandline that were not interpreted by #parse.
    attr_reader :leftovers

    ## The complete configuration hashes for each option. (Mainly useful
    ## for testing.)
    attr_reader :specs

    ## Initializes the parser, and instance-evaluates any block given.
    def initialize *a, &b
      @version = nil
      @leftovers = []
      @specs = {}
      @long = {}
      @short = {}
      @order = []
      @constraints = []
      @stop_words = []
      @stop_on_unknown = false

      #instance_eval(&b) if b # can't take arguments
      cloaker(&b).bind(self).call(*a) if b
    end

    ## Define an option. +name+ is the option name, a unique identifier
    ## for the option that you will use internally, which should be a
    ## symbol or a string. +desc+ is a string description which will be
    ## displayed in help messages.
    ##
    ## Takes the following optional arguments:
    ##
    ## [+:long+] Specify the long form of the argument, i.e. the form with two dashes. If unspecified, will be automatically derived based on the argument name by turning the +name+ option into a string, and replacing any _'s by -'s.
    ## [+:short+] Specify the short form of the argument, i.e. the form with one dash. If unspecified, will be automatically derived from +name+.
    ## [+:type+] Require that the argument take a parameter or parameters of type +type+. For a single parameter, the value can be a member of +SINGLE_ARG_TYPES+, or a corresponding Ruby class (e.g. +Integer+ for +:int+). For multiple-argument parameters, the value can be any member of +MULTI_ARG_TYPES+ constant. If unset, the default argument type is +:flag+, meaning that the argument does not take a parameter. The specification of +:type+ is not necessary if a +:default+ is given.
    ## [+:default+] Set the default value for an argument. Without a default value, the hash returned by #parse (and thus Trollop::options) will have a +nil+ value for this key unless the argument is given on the commandline. The argument type is derived automatically from the class of the default value given, so specifying a +:type+ is not necessary if a +:default+ is given. (But see below for an important caveat when +:multi+: is specified too.) If the argument is a flag, and the default is set to +true+, then if it is specified on the the commandline the value will be +false+.
    ## [+:required+] If set to +true+, the argument must be provided on the commandline.
    ## [+:multi+] If set to +true+, allows multiple occurrences of the option on the commandline. Otherwise, only a single instance of the option is allowed. (Note that this is different from taking multiple parameters. See below.)
    ##
    ## Note that there are two types of argument multiplicity: an argument
    ## can take multiple values, e.g. "--arg 1 2 3". An argument can also
    ## be allowed to occur multiple times, e.g. "--arg 1 --arg 2".
    ##
    ## Arguments that take multiple values should have a +:type+ parameter
    ## drawn from +MULTI_ARG_TYPES+ (e.g. +:strings+), or a +:default:+
    ## value of an array of the correct type (e.g. [String]). The
    ## value of this argument will be an array of the parameters on the
    ## commandline.
    ##
    ## Arguments that can occur multiple times should be marked with
    ## +:multi+ => +true+. The value of this argument will also be an array.
    ## In contrast with regular non-multi options, if not specified on
    ## the commandline, the default value will be [], not nil.
    ##
    ## These two attributes can be combined (e.g. +:type+ => +:strings+,
    ## +:multi+ => +true+), in which case the value of the argument will be
    ## an array of arrays.
    ##
    ## There's one ambiguous case to be aware of: when +:multi+: is true and a
    ## +:default+ is set to an array (of something), it's ambiguous whether this
    ## is a multi-value argument as well as a multi-occurrence argument.
    ## In thise case, Trollop assumes that it's not a multi-value argument.
    ## If you want a multi-value, multi-occurrence argument with a default
    ## value, you must specify +:type+ as well.

    def opt name, desc="", opts={}
      raise ArgumentError, "you already have an argument named '#{name}'" if @specs.member? name

      ## fill in :type
      opts[:type] = # normalize
          case opts[:type]
            when :boolean, :bool; :flag
            when :integer; :int
            when :integers; :ints
            when :double; :float
            when :doubles; :floats
            when Class
              case opts[:type].name
                when 'TrueClass', 'FalseClass'; :flag
                when 'String'; :string
                when 'Integer'; :int
                when 'Float'; :float
                when 'IO'; :io
                when 'Date'; :date
                else
                  raise ArgumentError, "unsupported argument type '#{opts[:type].class.name}'"
              end
            when nil; nil
            else
              raise ArgumentError, "unsupported argument type '#{opts[:type]}'" unless TYPES.include?(opts[:type])
              opts[:type]
          end

      ## for options with :multi => true, an array default doesn't imply
      ## a multi-valued argument. for that you have to specify a :type
      ## as well. (this is how we disambiguate an ambiguous situation;
      ## see the docs for Parser#opt for details.)
      disambiguated_default = if opts[:multi] && opts[:default].is_a?(Array) && !opts[:type]
                                opts[:default].first
                              else
                                opts[:default]
                              end

      type_from_default =
          case disambiguated_default
            when Integer; :int
            when Numeric; :float
            when TrueClass, FalseClass; :flag
            when String; :string
            when IO; :io
            when Date; :date
            when Array
              if opts[:default].empty?
                raise ArgumentError, "multiple argument type cannot be deduced from an empty array for '#{opts[:default][0].class.name}'"
              end
              case opts[:default][0]    # the first element determines the types
                when Integer; :ints
                when Numeric; :floats
                when String; :strings
                when IO; :ios
                when Date; :dates
                else
                  raise ArgumentError, "unsupported multiple argument type '#{opts[:default][0].class.name}'"
              end
            when nil; nil
            else
              raise ArgumentError, "unsupported argument type '#{opts[:default].class.name}'"
          end

      raise ArgumentError, ":type specification and default type don't match (default type is #{type_from_default})" if opts[:type] && type_from_default && opts[:type] != type_from_default

      opts[:type] = opts[:type] || type_from_default || :flag

      ## fill in :long
      opts[:long] = opts[:long] ? opts[:long].to_s : name.to_s.gsub("_", "-")
      opts[:long] = case opts[:long]
                      when /^--([^-].*)$/; $1
                      when /^[^-]/; opts[:long]
                      else; raise ArgumentError, "invalid long option name #{opts[:long].inspect}"
                    end
      raise ArgumentError, "long option name #{opts[:long].inspect} is already taken; please specify a (different) :long" if @long[opts[:long]]

      ## fill in :short
      opts[:short] = opts[:short].to_s if opts[:short] unless opts[:short] == :none
      opts[:short] = case opts[:short]
                       when /^-(.)$/; $1
                       when nil, :none, /^.$/; opts[:short]
                       else raise ArgumentError, "invalid short option name '#{opts[:short].inspect}'"
                     end

      if opts[:short]
        raise ArgumentError, "short option name #{opts[:short].inspect} is already taken; please specify a (different) :short" if @short[opts[:short]]
        raise ArgumentError, "a short option name can't be a number or a dash" if opts[:short] =~ INVALID_SHORT_ARG_REGEX
      end

      ## fill in :default for flags
      opts[:default] = false if opts[:type] == :flag && opts[:default].nil?

      ## autobox :default for :multi (multi-occurrence) arguments
      opts[:default] = [opts[:default]] if opts[:default] && opts[:multi] && !opts[:default].is_a?(Array)

      ## fill in :multi
      opts[:multi] ||= false

      opts[:desc] ||= desc
      @long[opts[:long]] = name
      @short[opts[:short]] = name if opts[:short] && opts[:short] != :none
      @specs[name] = opts
      @order << [:opt, name]
    end

    ## Sets the version string. If set, the user can request the version
    ## on the commandline. Should probably be of the form "<program name>
    ## <version number>".
    def version s=nil; @version = s if s; @version end

    ## Adds text to the help display. Can be interspersed with calls to
    ## #opt to build a multi-section help page.
    def banner s; @order << [:text, s] end
    alias :text :banner

    ## Marks two (or more!) options as requiring each other. Only handles
    ## undirected (i.e., mutual) dependencies. Directed dependencies are
    ## better modeled with Trollop::die.
    def depends *syms
      syms.each { |sym| raise ArgumentError, "unknown option '#{sym}'" unless @specs[sym] }
      @constraints << [:depends, syms]
    end

    ## Marks two (or more!) options as conflicting.
    def conflicts *syms
      syms.each { |sym| raise ArgumentError, "unknown option '#{sym}'" unless @specs[sym] }
      @constraints << [:conflicts, syms]
    end

    ## Defines a set of words which cause parsing to terminate when
    ## encountered, such that any options to the left of the word are
    ## parsed as usual, and options to the right of the word are left
    ## intact.
    ##
    ## A typical use case would be for subcommand support, where these
    ## would be set to the list of subcommands. A subsequent Trollop
    ## invocation would then be used to parse subcommand options, after
    ## shifting the subcommand off of ARGV.
    def stop_on *words
      @stop_words = [*words].flatten
    end

    ## Similar to #stop_on, but stops on any unknown word when encountered
    ## (unless it is a parameter for an argument). This is useful for
    ## cases where you don't know the set of subcommands ahead of time,
    ## i.e., without first parsing the global options.
    def stop_on_unknown
      @stop_on_unknown = true
    end

    ## Parses the commandline. Typically called by Trollop::options,
    ## but you can call it directly if you need more control.
    ##
    ## throws CommandlineError, HelpNeeded, and VersionNeeded exceptions.
    def parse cmdline=ARGV
      vals = {}
      required = {}

      opt :version, "Print version and exit" if @version unless @specs[:version] || @long["version"]
      opt :help, "Show this message" unless @specs[:help] || @long["help"]

      @specs.each do |sym, opts|
        required[sym] = true if opts[:required]
        vals[sym] = opts[:default]
        vals[sym] = [] if opts[:multi] && !opts[:default] # multi arguments default to [], not nil
      end

      resolve_default_short_options!

      ## resolve symbols
      given_args = {}
      @leftovers = each_arg cmdline do |arg, params|
        ## handle --no- forms
        arg, negative_given = if arg =~ /^--no-([^-]\S*)$/
                                ["--#{$1}", true]
                              else
                                [arg, false]
                              end

        sym = case arg
                when /^-([^-])$/; @short[$1]
                when /^--([^-]\S*)$/; @long[$1] || @long["no-#{$1}"]
                else; raise CommandlineError, "invalid argument syntax: '#{arg}'"
              end

        sym = nil if arg =~ /--no-/ # explicitly invalidate --no-no- arguments

        raise CommandlineError, "unknown argument '#{arg}'" unless sym

        if given_args.include?(sym) && !@specs[sym][:multi]
          raise CommandlineError, "option '#{arg}' specified multiple times"
        end

        given_args[sym] ||= {}
        given_args[sym][:arg] = arg
        given_args[sym][:negative_given] = negative_given
        given_args[sym][:params] ||= []

        # The block returns the number of parameters taken.
        num_params_taken = 0

        unless params.nil?
          if SINGLE_ARG_TYPES.include?(@specs[sym][:type])
            given_args[sym][:params] << params[0, 1]  # take the first parameter
            num_params_taken = 1
          elsif MULTI_ARG_TYPES.include?(@specs[sym][:type])
            given_args[sym][:params] << params        # take all the parameters
            num_params_taken = params.size
          end
        end

        num_params_taken
      end

      ## check for version and help args
      raise VersionNeeded if given_args.include? :version
      raise HelpNeeded if given_args.include? :help

      ## check constraint satisfaction
      @constraints.each do |type, syms|
        constraint_sym = syms.find { |sym| given_args[sym] }
        next unless constraint_sym

        case type
          when :depends
            syms.each { |sym| raise CommandlineError, "--#{@specs[constraint_sym][:long]} requires --#{@specs[sym][:long]}" unless given_args.include? sym }
          when :conflicts
            syms.each { |sym| raise CommandlineError, "--#{@specs[constraint_sym][:long]} conflicts with --#{@specs[sym][:long]}" if given_args.include?(sym) && (sym != constraint_sym) }
        end
      end

      required.each do |sym, val|
        raise CommandlineError, "option --#{@specs[sym][:long]} must be specified" unless given_args.include? sym
      end

      ## parse parameters
      given_args.each do |sym, given_data|
        arg, params, negative_given = given_data.values_at :arg, :params, :negative_given

        opts = @specs[sym]
        raise CommandlineError, "option '#{arg}' needs a parameter" if params.empty? && opts[:type] != :flag

        vals["#{sym}_given".intern] = true # mark argument as specified on the commandline

        case opts[:type]
          when :flag
            vals[sym] = (sym.to_s =~ /^no_/ ? negative_given : !negative_given)
          when :int, :ints
            vals[sym] = params.map { |pg| pg.map { |p| parse_integer_parameter p, arg } }
          when :float, :floats
            vals[sym] = params.map { |pg| pg.map { |p| parse_float_parameter p, arg } }
          when :string, :strings
            vals[sym] = params.map { |pg| pg.map { |p| p.to_s } }
          when :io, :ios
            vals[sym] = params.map { |pg| pg.map { |p| parse_io_parameter p, arg } }
          when :date, :dates
            vals[sym] = params.map { |pg| pg.map { |p| parse_date_parameter p, arg } }
        end

        if SINGLE_ARG_TYPES.include?(opts[:type])
          unless opts[:multi]       # single parameter
            vals[sym] = vals[sym][0][0]
          else                      # multiple options, each with a single parameter
            vals[sym] = vals[sym].map { |p| p[0] }
          end
        elsif MULTI_ARG_TYPES.include?(opts[:type]) && !opts[:multi]
          vals[sym] = vals[sym][0]  # single option, with multiple parameters
        end
        # else: multiple options, with multiple parameters
      end

      ## modify input in place with only those
      ## arguments we didn't process
      cmdline.clear
      @leftovers.each { |l| cmdline << l }

      ## allow openstruct-style accessors
      class << vals
        def method_missing(m, *args)
          self[m] || self[m.to_s]
        end
      end
      vals
    end

    def parse_date_parameter param, arg #:nodoc:
      begin
        begin
          time = Chronic.parse(param)
        rescue NameError
          # chronic is not available
        end
        time ? Date.new(time.year, time.month, time.day) : Date.parse(param)
      rescue ArgumentError
        raise CommandlineError, "option '#{arg}' needs a date"
      end
    end

    ## Print the help message to +stream+.
    def educate stream=$stdout
      width # hack: calculate it now; otherwise we have to be careful not to
      # call this unless the cursor's at the beginning of a line.
      left = {}
      @specs.each do |name, spec|
        left[name] = "--#{spec[:long]}" +
            (spec[:type] == :flag && spec[:default] ? ", --no-#{spec[:long]}" : "") +
            (spec[:short] && spec[:short] != :none ? ", -#{spec[:short]}" : "") +
            case spec[:type]
              when :flag; ""
              when :int; " <i>"
              when :ints; " <i+>"
              when :string; " <s>"
              when :strings; " <s+>"
              when :float; " <f>"
              when :floats; " <f+>"
              when :io; " <filename/uri>"
              when :ios; " <filename/uri+>"
              when :date; " <date>"
              when :dates; " <date+>"
            end
      end

      leftcol_width = left.values.map { |s| s.length }.max || 0
      rightcol_start = leftcol_width + 6 # spaces

      unless @order.size > 0 && @order.first.first == :text
        stream.puts "#@version\n" if @version
        stream.puts "Options:"
      end

      @order.each do |what, opt|
        if what == :text
          stream.puts wrap(opt)
          next
        end

        spec = @specs[opt]
        stream.printf "  %#{leftcol_width}s:   ", left[opt]
        desc = spec[:desc] + begin
          default_s = case spec[:default]
                        when $stdout; "<stdout>"
                        when $stdin; "<stdin>"
                        when $stderr; "<stderr>"
                        when Array
                          spec[:default].join(", ")
                        else
                          spec[:default].to_s
                      end

          if spec[:default]
            if spec[:desc] =~ /\.$/
              " (Default: #{default_s})"
            else
              " (default: #{default_s})"
            end
          else
            ""
          end
        end
        stream.puts wrap(desc, :width => width - rightcol_start - 1, :prefix => rightcol_start)
      end
    end

    def width #:nodoc:
      @width ||= if $stdout.tty?
                   begin
                     require 'curses'
                     Curses::init_screen
                     x = Curses::cols
                     Curses::close_screen
                     x
                   rescue Exception
                     80
                   end
                 else
                   80
                 end
    end

    def wrap str, opts={} # :nodoc:
      if str == ""
        [""]
      else
        str.split("\n").map { |s| wrap_line s, opts }.flatten
      end
    end

    ## The per-parser version of Trollop::die (see that for documentation).
    def die arg, msg
      if msg
        $stderr.puts "Error: argument --#{@specs[arg][:long]} #{msg}."
      else
        $stderr.puts "Error: #{arg}."
      end
      $stderr.puts "Try --help for help."
      exit(-1)
    end

    private

    ## yield successive arg, parameter pairs
    def each_arg args
      remains = []
      i = 0

      until i >= args.length
        if @stop_words.member? args[i]
          remains += args[i .. -1]
          return remains
        end
        case args[i]
          when /^--$/ # arg terminator
            remains += args[(i + 1) .. -1]
            return remains
          when /^--(\S+?)=(.*)$/ # long argument with equals
            yield "--#{$1}", [$2]
            i += 1
          when /^--(\S+)$/ # long argument
            params = collect_argument_parameters(args, i + 1)
            unless params.empty?
              num_params_taken = yield args[i], params
              unless num_params_taken
                if @stop_on_unknown
                  remains += args[i + 1 .. -1]
                  return remains
                else
                  remains += params
                end
              end
              i += 1 + num_params_taken
            else # long argument no parameter
              yield args[i], nil
              i += 1
            end
          when /^-(\S+)$/ # one or more short arguments
            shortargs = $1.split(//)
            shortargs.each_with_index do |a, j|
              if j == (shortargs.length - 1)
                params = collect_argument_parameters(args, i + 1)
                unless params.empty?
                  num_params_taken = yield "-#{a}", params
                  unless num_params_taken
                    if @stop_on_unknown
                      remains += args[i + 1 .. -1]
                      return remains
                    else
                      remains += params
                    end
                  end
                  i += 1 + num_params_taken
                else # argument no parameter
                  yield "-#{a}", nil
                  i += 1
                end
              else
                yield "-#{a}", nil
              end
            end
          else
            if @stop_on_unknown
              remains += args[i .. -1]
              return remains
            else
              remains << args[i]
              i += 1
            end
        end
      end

      remains
    end

    def parse_integer_parameter param, arg
      raise CommandlineError, "option '#{arg}' needs an integer" unless param =~ /^\d+$/
      param.to_i
    end

    def parse_float_parameter param, arg
      raise CommandlineError, "option '#{arg}' needs a floating-point number" unless param =~ FLOAT_RE
      param.to_f
    end

    def parse_io_parameter param, arg
      case param
        when /^(stdin|-)$/i; $stdin
        else
          require 'open-uri'
          begin
            open param
          rescue SystemCallError => e
            raise CommandlineError, "file or url for option '#{arg}' cannot be opened: #{e.message}"
          end
      end
    end

    def collect_argument_parameters args, start_at
      params = []
      pos = start_at
      while args[pos] && args[pos] !~ PARAM_RE && !@stop_words.member?(args[pos]) do
        params << args[pos]
        pos += 1
      end
      params
    end

    def resolve_default_short_options!
      @order.each do |type, name|
        next unless type == :opt
        opts = @specs[name]
        next if opts[:short]

        c = opts[:long].split(//).find { |d| d !~ INVALID_SHORT_ARG_REGEX && !@short.member?(d) }
        if c # found a character to use
          opts[:short] = c
          @short[c] = name
        end
      end
    end

    def wrap_line str, opts={}
      prefix = opts[:prefix] || 0
      width = opts[:width] || (self.width - 1)
      start = 0
      ret = []
      until start > str.length
        nextt =
            if start + width >= str.length
              str.length
            else
              x = str.rindex(/\s/, start + width)
              x = str.index(/\s/, start) if x && x < start
              x || str.length
            end
        ret << (ret.empty? ? "" : " " * prefix) + str[start ... nextt]
        start = nextt + 1
      end
      ret
    end

    ## instance_eval but with ability to handle block arguments
    ## thanks to _why: http://redhanded.hobix.com/inspect/aBlockCostume.html
    def cloaker &b
      (class << self; self; end).class_eval do
        define_method :cloaker_, &b
        meth = instance_method :cloaker_
        remove_method :cloaker_
        meth
      end
    end
  end

## The easy, syntactic-sugary entry method into Trollop. Creates a Parser,
## passes the block to it, then parses +args+ with it, handling any errors or
## requests for help or version information appropriately (and then exiting).
## Modifies +args+ in place. Returns a hash of option values.
##
## The block passed in should contain zero or more calls to +opt+
## (Parser#opt), zero or more calls to +text+ (Parser#text), and
## probably a call to +version+ (Parser#version).
##
## The returned block contains a value for every option specified with
## +opt+.  The value will be the value given on the commandline, or the
## default value if the option was not specified on the commandline. For
## every option specified on the commandline, a key "<option
## name>_given" will also be set in the hash.
##
## Example:
##
##   require 'trollop'
##   opts = Trollop::options do
##     opt :monkey, "Use monkey mode"                    # a flag --monkey, defaulting to false
##     opt :name, "Monkey name", :type => :string        # a string --name <s>, defaulting to nil
##     opt :num_limbs, "Number of limbs", :default => 4  # an integer --num-limbs <i>, defaulting to 4
##   end
##
##   ## if called with no arguments
##   p opts # => {:monkey=>false, :name=>nil, :num_limbs=>4, :help=>false}
##
##   ## if called with --monkey
##   p opts # => {:monkey=>true, :name=>nil, :num_limbs=>4, :help=>false, :monkey_given=>true}
##
## See more examples at http://trollop.rubyforge.org.
  def options args=ARGV, *a, &b
    @last_parser = Parser.new(*a, &b)
    with_standard_exception_handling(@last_parser) { @last_parser.parse args }
  end

## If Trollop::options doesn't do quite what you want, you can create a Parser
## object and call Parser#parse on it. That method will throw CommandlineError,
## HelpNeeded and VersionNeeded exceptions when necessary; if you want to
## have these handled for you in the standard manner (e.g. show the help
## and then exit upon an HelpNeeded exception), call your code from within
## a block passed to this method.
##
## Note that this method will call System#exit after handling an exception!
##
## Usage example:
##
##   require 'trollop'
##   p = Trollop::Parser.new do
##     opt :monkey, "Use monkey mode"                     # a flag --monkey, defaulting to false
##     opt :goat, "Use goat mode", :default => true       # a flag --goat, defaulting to true
##   end
##
##   opts = Trollop::with_standard_exception_handling p do
##     o = p.parse ARGV
##     raise Trollop::HelpNeeded if ARGV.empty? # show help screen
##     o
##   end
##
## Requires passing in the parser object.

  def with_standard_exception_handling parser
    begin
      yield
    rescue CommandlineError => e
      $stderr.puts "Error: #{e.message}."
      $stderr.puts "Try --help for help."
      exit(-1)
    rescue HelpNeeded
      parser.educate
      exit
    rescue VersionNeeded
      puts parser.version
      exit
    end
  end

## Informs the user that their usage of 'arg' was wrong, as detailed by
## 'msg', and dies. Example:
##
##   options do
##     opt :volume, :default => 0.0
##   end
##
##   die :volume, "too loud" if opts[:volume] > 10.0
##   die :volume, "too soft" if opts[:volume] < 0.1
##
## In the one-argument case, simply print that message, a notice
## about -h, and die. Example:
##
##   options do
##     opt :whatever # ...
##   end
##
##   Trollop::die "need at least one filename" if ARGV.empty?
  def die arg, msg=nil
    if @last_parser
      @last_parser.die arg, msg
    else
      raise ArgumentError, "Trollop::die can only be called after Trollop::options"
    end
  end

  module_function :options, :die, :with_standard_exception_handling

end # module
